The correct Aeronca K propeller is unique in that the 6 bolt holes are 30 degrees different than traditional wood propellers. This is because of the 2-cylinder Aeronca E-113 engine. Most other 6-hole wood propellers have two of the holes aligned with the length of the propeller. But the correct propeller for the E-113 has two of the holes perpendicular to the center line of the propeller, which is 30 degrees rotated from most other propellers used on 4-cylinder engines. This allignment of the holes is required in order to have the propeller in the proper position (on the Aeronca E-113 engine) to hand prop the airplane. This is not the case for the Continential A-65 where the compression stroke and impulse release occurs in a different position.
Although an incorrect propeller (with the holes driller 30 degrees from the correct location) will still make the airplane fly, it is more dangerous to hand-prop since the propeller is in the wrong location. That is, the propeller is in the 12 O'clock position upon the start of compression.
Sensenich currently sells the W69A-28 and W69A-30 for the Aeronca E-113 series engine, however, their drawings have the bolt holes in the wrong location. If you purchase the standard W69A-28 or W69A-30 they will manufacture it to the drawings, which will be the wrong propeller for your E-113.
Good news: On August 8, 2000, I spoke with Charlie in the Wood Propeller division of Sensenich. In short, Sensenich agreed to change the drawings, but it may take a few years. In the meantime, they will manufacture the correct propellers using a special MRB process that allows them to put the holes in the correct location. When ordering a W69A-28 or W69A-30 from Sensenich you must ask for the the MRB process to have the holes drilled correctly. See below for full details on my conversation with Charlie at Sensenich.
Below are some pictures to show (prove) the correct bolt hole locations.
 Tom Trainor's K-244 |
 From John Taylor K-180 |
  Dave Johnson K-50 |
 From the E-113 Engine Manual Page 12. |
Here is a review of my conversation with Sensenich today, 8/8/00.
I talked to Charlie at 813-752-3711. He was very pleasant to work with.
Yesterday I explained the situation with the E-113 engines and the required location of
the bolt holes. I showed him the website with the pictures of existing props. I asked if
Sensenich would be willing to make a prop like this, although the technical drawing he
faxed me in June have the holes in the wrong location. He agreed to look into it. He
expected the problem would be more with the FAA than with Sensenich.
Later that day, he determined that the technical drawing that he faxed me in June has a
1944 date. So the drawing has been wrong for many years. I also explained that Tom Trainor
had purchased a prop from them in 1992 with the holes drilled correctly, that is now
mounted on K-244 at the Pioneer Museum in Oshkosh. So at one time, in the late 1930s when
the E-113s were being sold new by Aeronca, and in 1992, Sensenich was willing to make the
propellers correctly. Thus they must already have FAA approval and thus, it seams to me,
the FAA need not get involved.
Today when I called him back he provided the following good news:
After talking to the General Manager (Don) and the Quality Control person (Hearld),
Sensenich agreed that the drawings need to be changed. However, it may take a year or more
to make those changes since it is not a priority. In the mean time, Sensenich agreed to
make the W69A-28 and W69A-30 with the correct bolt holes (as we describe) using the MRB
process.
The Manufacturing Review Board (MRB) process is the approved method for manufacturing
certified propellers that are not made to drawing specifications. Props made out of
drawing specs are reviewed by the MRB for safety. If the MRB determines that the
non-compliant prop (such as the holes drilled 30 degrees off from the drawings) will still
operate safely, then the prop is stamped near the hub with an "MRB" stamp and
the prop is released.